Question about mobile array 4 x 455w panels - 4S or 2S2P and SCC sizing?

[Mr. Eddie]

Hello all -
New to solar, but installed phone systems for 30+ years, and think I can build/install a solar system on my trailer. Just hold my beer... ;D
I looked at many hours of video, and searched this site for a TON of great information (thanks y'all), but still have a few questions at this point. I plan to do a considerable amount of boondocking, almost exclusively in the western US, Canada, and Mexico. I'll be building my own 234v battery using EVE 314ah cells from Docan (less than $80 each as of 9-15-2024) and hopefully using new Solar Ever 455w panels with these specs:

• Power: 455W
• Maximum Voltage (VMP): 41.51 V
• Maximum Power Current (IMP): 10.96 A
• Open Circuit Voltage (VOC): 49.35 V
• Short Circuit Current (ISC): 11.44 A
• Maximum Fuse Rating: 20 A
• Maximum System Voltage: 1500VDC (IEC)
• Dimensions: 82.44 in x 40.86 in x 1.37
• Weight: 51.8 lbs.

I'd planned on a 2S2P configuration, based on a consensus of opinions, but recently read that modern panels have diodes built in to allow for some solution to the shading issues of series connections. If I go with a 4S setup instead, this will, I believe, make a huge difference in the MPPT controller I will need. With the above specs, a 2S2P configuration would give me a nominal 88.70 VOC and a 22.88 ISC. I was considering a Victron SmartSolar 150/60, since the lowest temps I'll see while travelling will be around 28 F, and I'll never exceed my VOC rating.

With a 4S configuration, it looks like my VOC will 197.40, and the Victron 150/60 won't work. the 250/60 would work, but the cost difference is about $65-$70 more, with a slightly bigger footprint.

Is there any advantage in going with a 4S versus a 2S2P configuration(aside from the increased voltage to the SCC series gives me)? Should I be concerned enough about shading to stick with a 2S2P setup?

Thanks in advance!


Eddie

 

[HRTKD]

I don't think you're building a 234v battery. But we do need to know the system voltage: 12v, 24v or 48v?

Four 455w panels will produce at most 151 amps on a 12 volt system. (455 x 4) / 12 = 151. That's a pretty big solar charge controller.

If you have a 24 volt system it would cut the amps in half to ~75 amps. Still pretty high.

You could use two Victron 100/50 controllers with two panels in series in on each controller. But on a 12 volt system you would still be leaving amps on the table. This is the main reason I decided to go with a 48 volt system for my current build. I'm using a Victron 150/35 with either 2s2p or 3s when using a second controller.

The only shading that I take into account in my design is from the A/C unit on the roof.

Are you using the Victron MPPT Calculator? If not, it's a great resource.

 

[Mr. Eddie]

I don't think you're building a 234v battery. But we do need to know the system voltage: 12v, 24v or 48v?

Four 455w panels will produce at most 151 amps on a 12 volt system. (455 x 4) / 12 = 151. That's a pretty big solar charge controller.

If you have a 24 volt system it would cut the amps in half to ~75 amps. Still pretty high.

You could use two Victron 100/50 controllers with two panels in series in on each controller. But on a 12 volt system you would still be leaving amps on the table. This is the main reason I decided to go with a 48 volt system for my current build. I'm using a Victron 150/35 with either 2s2p or 3s when using a second controller.

The only shading that I take into account in my design is from the A/C unit on the roof.

Are you using the Victron MPPT Calculator? If not, it's a great resource.

Duh... I'm a dumbass for not checking my typing. I meant to type in 24v system instead of 234v.

I hadn't considered a 48v system, because of cost and footprint. I'll have a "portable" 2 x 100w panels in series with an extension cable and a small MPPT for days when I'm under or blocked by trees, and as a backup. It may be overkill, and I'm still working out the wiring and connections.

I know it's a big system for mobile applications, but I don't plan on staying at campgrounds except on rare occasions, and thought that this design would be more than adequate.

 

[Rocketman]

Go 2s2p to save the $$$.

There will be some marginal times 4s would be slightly better - there will be some marginal times 2s2p will be better. You probably will never notice the difference if you setup your system so you could trade it each day.

In this case $$$ rules. The 150/60 will be slightly overpaneled- but if it’s anything like my system- you very seldom see it maxed.

 

[Mr. Eddie]

There are more light bulbs beginning to go off over my head...

Two controllers allows me to reduce the amperage across the circuit, thus allowing a lower level for wiring, fuses, etc. My SCC footprint increases, and also my wiring, but I can manage those changes. I didn't see earlier that the Victron controller only lets you use a max 6ga wire to run to the battery. Two controllers solves that issue. Panel wiring to the SCC will be 10ga, and then 6ga to the power distribution buss/battery, with a fuse from each SCC to the buss.

 

[Mr. Eddie]

Go 2s2p to save the $$$.

There will be some marginal times 4s would be slightly better - there will be some marginal times 2s2p will be better. You probably will never notice the difference if you setup your system so you could trade it each day.

In this case $$$ rules. The 150/60 will be slightly overpaneled- but if it’s anything like my system- you very seldom see it maxed.

I am still reading up on overpanneling - apparently, it's not a bad thing if it's only slightly overpanneled. Especially considering that even adjusting for cold temps, real world results are not going to meet the paper specs for many hours of the day.

I'm not sure what you mean by setting up my system so that I can "trade it each day". My panels will be mounted flat, 10" above my trailer roof, and the wiring will be fixed in length and connection points. Part of the reason I am choosing such big panels is to keep my panel mounting simple and robust - no tilting, even though I know this is not the most efficient choice. It does, however, seem to be a very secure option, since the panels will be bolted down to a ladder rack rail.

Does the "trading" involve software or hardware reconfigurations?

 

[HRTKD]

I'm not sure what you mean by setting up my system so that I can "trade it each day".

I think he meant that if you could easily switch between 4s and 2s2p, you wouldn't see much difference.

Part of the reason I am choosing such big panels is to keep my panel mounting simple and robust - no tilting

Welcome to the Flat Panel Society. We may not be optimal, but we're simple.

 

[Rednecktek]

10" above my trailer roof,

That's a LOT of uplift and wiggle driving down the road. On my trailer I might have 2" and I was worried the first couple drives out to the mountains.

455w × 4 = 1820w ÷ 24v = about 75a. I wouldn't go less than a 60a or a pair of 40a units if you ran 2 sets of panels. If you go with a single SCC, go 2s2p and you're good.

I'll have a "portable" 2 x 100w panels in series with an extension cable and a small MPPT for days when I'm under or blocked by trees

200w of panel isn't much, you can get a pair of folding 200+ watt panels for the same-ish weight and bulk. 200w × 4 hours (at best, stupid trees) = 800wh ÷ 24v = 33ah best case back into the batteries.

I was considering a Victron SmartSolar 150/60

Don't think $$Victron is the only option no matter what the smurfs say. You can get an HQST 150/60 with the same specs AND a display screen AND physical buttons for 1/3 less. It will still turn solar DC into battery DC just fine but for $100+ less.

I am still reading up on overpanneling - apparently, it's not a bad thing if it's only slightly overpanneled. Especially considering that even adjusting for cold temps, real world results are not going to meet the paper specs for many hours of the day.

Overpaneling is handy, especially if you're boondocking anywhere other than the desert in summer. Trees nerf panels quick and not being able to aim the roof will cut down on productivity as well. Even in summer in the desert in a snowstorm on the summer solstice if you were somehow to reach maximum wattage, the little bit of clipping wouldn't be enough to worry about the other 363 days a year.

 

[Rocketman]

I think he meant that if you could easily switch between 4s and 2s2p, you wouldn't see much difference.



Welcome to the Flat Panel Society. We may not be optimal, but we're simple.

That is exactly what I ment (and did not type well).

My opinion on Victron (from a Smurf team member), if you are only getting one item a Solar charge controller then it may not be worth the extra cost for Victron products- (just don’t buy a junk product). But if you will be doing lots (shunt,invert, and solar), the way Victron ties stuff together makes it worth it (to me).

 

[Mr. Eddie]

Good points all...

My experiences with phone systems taught me that wiring - once installed PROPERLY - is rarely a point of failure in electronic circuits. Not so sure if that holds true with electrical circuits. I have done some 12 VDC wiring on various sailboats, so crimping, heat shrink, ABYC tables, etc. are very familiar. I have a preference for Ancor marine-grade wire and associated components, Blue Seas fuse holders/power distribution buss, 3000w psw Giandell 24v inverter, but am opting for an inexpensive set of panels through SanTan Solar (455w panel is $189, which is wallet friendly, for certain). They don't have any used panels that size just now, but I'm not adding the permanent panels on the roof until next May. The 200-400w el cheapo set will get me down to Phoenix and I'll install the big boys there.

Originally, after reading Will Prowse's info, my plan was to go with the Epever Tracer BN SCC that he recommends, simply because of the robust connections. But then I looked at the max array wattage limits, and checked into other single SCC solutions. I had heard Victron "Smurf" products being touted as excellent stuff, and while I like excellence, I know you don't always have to pay the most money to get excellence. I'll certainly look into alternatives. Reliability and ease of operation are the most important features for me, especially reliability, since I'll be off pavement quite a bit.

As far as the 10" choice, the Maxxair fan cover tops out at 9.something" above the roofline. I don't want to shade the panels with anything if I can help it. I'll keep the speed down to 60mph or less - I'll be retired and in no hurry on my adventures, so hopefully I won't be experimenting with solar wings! The panels will almost span the width of the trailer, and have about 3" between them, running fore and aft about 16' in total length. I haven't spoken with anyone in person who has a large array on their rig that hasn't used VHB tape to adhere the panels directly to to roof (this person is rethinking that idea, and dreading the removal of a few thousand dollars of beautiful flexible panels).

I could always start with 2 panels to see how it handles...

 

[Brucey]

6AWG

There are more light bulbs beginning to go off over my head...

Two controllers allows me to reduce the amperage across the circuit, thus allowing a lower level for wiring, fuses, etc. My SCC footprint increases, and also my wiring, but I can manage those changes. I didn't see earlier that the Victron controller only lets you use a max 6ga wire to run to the battery. Two controllers solves that issue. Panel wiring to the SCC will be 10ga, and then 6ga to the power distribution buss/battery, with a fuse from each SCC to the buss.

The 150/35 and 150/45 have a max of 6AWG.

The 150/60 and 70 allow for 2AWG.

Multiple smaller controllers are nice for managing shade, and giving you redundancy in case of a rare failure.

 

[Brucey]

Originally, after reading Will Prowse's info, my plan was to go with the Epever Tracer BN SCC that he recommends, simply because of the robust connections. But then I looked at the max array wattage limits, and checked into other single SCC solutions. I had heard Victron "Smurf" products being touted as excellent stuff, and while I like excellence, I know you don't always have to pay the most money to get excellence. I'll certainly look into alternatives. Reliability and ease of operation are the most important features for me, especially reliability, since I'll be off pavement quite a bit.

Other thing with the Smurf tech is Victron Connect app via Bluetooth for grabbing all the per second updates of power production etc. And then that's a gateway drug into a full VRM system down the track on a cerbo or pi running venus os. Also if you happen to have an issue out in a remote area much more likely to be a Victron dealer around.

There used to be a large gulf between Victron and some of the other SCCs but after big price drops last year the Delta isn't much for the benefits imo.

 

[Mr. Eddie]

Oh man, Brucey.

Once you said " gateway drug" and "cerbo", my brain started spinning and I saw a deep rabbit hole open up and beckon me to enter within and explore the realm of... I had to stop there, and go back to taking the little steps to battery assembly and top balancing and capacity testing. Whew!

I do like the idea of redundancy, from a reliability perspective. The cost for that is really not much different than a single scc, at least in Smurf tech.

Since this is my first experience in the Flat Panel Society world, I am relying on those of you with much greater knowledge for some recommendations and a bit of guidance, knowing that I will have to decide what will be best for my system.

And thanks, in advance.

 

[TheBreeze]

I'm going down a similar path and closely following this thread. I'm nearing the end of my design and looking to size a charge controller too.

The application is an RV not much unlike yours. I won't likely expand the panels as I'm out of room. I chose 2S2P based on mixed circumstances (sun and shade - it's an RV). I have 4-445w panels. The inverter is 2500w AIMS backed by 4-Battle Born 100Amp. I may expand the bank but the solar is less likely unless I want to drag around portables with no place to store them.

Won't be going to 24 or 48 volt system just to step it down to 12v in the end. I can't see creating all those volts just to throw them away later. The inverter is there to run the microwave, a toaster, toaster oven and induction cooktop on 110v. Everything else is 12v. Nothing really beyond that except maybe A/C with a soft start (but that's a stretch).

I calculate a 75A charge controller based on 2S2P and the calculation: 890W/12V=75A.

Design:
4 panels, 2 arrays.
2 panels in series, 2 arrays in parallel.

Array:
TW: 445
TA: 26.96 (ISC)
TV: 41.9 (VOC)

Total In:
TW: 890
TA: 26.96 (ISC)
TV: 83.8 (VOC)


Full Panel Spec

Power: 445W
Efficiency: 20.14%
Open Circuit Voltage (VOC): 41.9 V
Short Circuit Current (ISC): 13.48 A
Maximum Power Voltage (VMP): 34.8 V
Maximum Power Current (IMP): 12.79 A
Maximum Series Fuse Rating: 30 A
Maximum System Voltage: 1000 V

 

[Mr. Eddie]

I'm going down a similar path and closely following this thread. I'm nearing the end of my design and looking to size a charge controller too.

The application is an RV not much unlike yours. I won't likely expand the panels as I'm out of room. I chose 2S2P based on mixed circumstances (sun and shade - it's an RV). I have 4-445w panels. The inverter is 2500w AIMS backed by 4-Battle Born 100Amp. I may expand the bank but the solar is less likely unless I want to drag around portables with no place to store them.

Won't be going to 24 or 48 volt system just to step it down to 12v in the end. I can't see creating all those volts just to throw them away later. The inverter is there to run the microwave, a toaster, toaster oven and induction cooktop on 110v. Everything else is 12v. Nothing really beyond that except maybe A/C with a soft start (but that's a stretch).

I calculate a 75A charge controller based on 2S2P and the calculation: 890W/12V=75A.

Design:
4 panels, 2 arrays.
2 panels in series, 2 arrays in parallel.

Array:
TW: 445
TA: 13.48 (ISC)
TV: 83.8 (VOC)

Total In:
TW: 890
TA: 26.96 (ISC)
TV: 83.8 (VOC)


Full Panel Spec

Power: 445W
Efficiency: 20.14%
Open Circuit Voltage (VOC): 41.9 V
Short Circuit Current (ISC): 13.48 A
Maximum Power Voltage (VMP): 34.8 V
Maximum Power Current (IMP): 12.79 A
Maximum Series Fuse Rating: 30 A
Maximum System Voltage: 1000 V

Hello -
I'm not sure what you mean by "throwing them away", unless you're referring to the slight loss in going from 24v to 12v. I'm sure more knowledgeable folks can weigh in here. I'll be running a 110ac fridge and eventually a 120 A/C mini split and a 3000w psw inverter. 24v was recommended for a number of reasons

 

[TheBreeze]

Hello -
I'm not sure what you mean by "throwing them away", unless you're referring to the slight loss in going from 24v to 12v. I'm sure more knowledgeable folks can weigh in here. I'll be running a 110ac fridge and eventually a 120 A/C mini split and a 3000w psw inverter. 24v was recommended for a number of reasons

Hi

What I'm really after is if I read the panel specs correctly. Do I use the panel combined watts to size the SCC in which case I use the 75A calculation, or use the VOC on a 2S2P configuration which gets me down below 30A?

 

[Rocketman]

With those four panels, mounted flat, I would use either a Victron 150/100 or two arrays and either two 100/50’s or two 150/60’s.

Here is the math…
Four 445w panels…
4x445= 1780watts
1780w / 14.4v = 123amps of power at 14.4v

So using a Victron 150/100, you will be a bit over paneled. If you want to capture every possible watt, then go with the two panels on an array (either series or parallel), and put them into a 150/60. (You will need two of the 150/60 - one for each array of two panels). From the Victron data sheet - it can output 860watts on a 12v system - which is really close to the 890w your panels can produce.

The cheapest option will be to use two mppt 100/50’s.

You probably need to decide if it is worth it to occasionally charge above 100amps when the sun is really out. My guess is it would not be worth it. When the sun is really out you will charge your batteries up really quickly… about 3hrs from 25% to full. If you charge at 120amps it would only take 2.5hrs from 25% to full. After the batteries are full - it all that potential power is lost.

Back to math.
You use the Voc to make sure you will never put more voltage into the mppt than it can handle.
Voc 41.9v with two in series 41.9times 2 = 83.8v. This has enough buffer that you be ok using 2s into the mppt 100/50.

To calculate the array voltage and amps and watts you use the Vmp and Imp
Vmp 34.8v
Imp 12.79a
With 2s2p going into the mppt 150/100 this is what it will look like.
2 in series - 34.8 + 34.8 = 69.6v and 12.79a.
Those two 2s put in parallel you add the amps - so 69.6v and 12.79 + 12.79 = 25.58amps
Volts * amps = watts
69.6 * 25.58 = 1.780 watts

From the data sheet - the max the mppt 150/100 can output is 1450watts - so everything about that will be clipped. But times that are partially cloudy or not perfect conditions- you will have the advantage of more panels on the roof.

Did this long post answer your questions?

 

[Mr. Eddie]

With those four panels, mounted flat, I would use either a Victron 150/100 or two arrays and either two 100/50’s or two 150/60’s.

Here is the math…
Four 445w panels…
4x445= 1780watts
1780w / 14.4v = 123amps of power at 14.4v

So using a Victron 150/100, you will be a bit over paneled. If you want to capture every possible watt, then go with the two panels on an array (either series or parallel), and put them into a 150/60. (You will need two of the 150/60 - one for each array of two panels). From the Victron data sheet - it can output 860watts on a 12v system - which is really close to the 890w your panels can produce.

The cheapest option will be to use two mppt 100/50’s.

You probably need to decide if it is worth it to occasionally charge above 100amps when the sun is really out. My guess is it would not be worth it. When the sun is really out you will charge your batteries up really quickly… about 3hrs from 25% to full. If you charge at 120amps it would only take 2.5hrs from 25% to full. After the batteries are full - it all that potential power is lost.

Back to math.
You use the Voc to make sure you will never put more voltage into the mppt than it can handle.
Voc 41.9v with two in series 41.9times 2 = 83.8v. This has enough buffer that you be ok using 2s into the mppt 100/50.

To calculate the array voltage and amps and watts you use the Vmp and Imp
Vmp 34.8v
Imp 12.79a
With 2s2p going into the mppt 150/100 this is what it will look like.
2 in series - 34.8 + 34.8 = 69.6v and 12.79a.
Those two 2s put in parallel you add the amps - so 69.6v and 12.79 + 12.79 = 25.58amps
Volts * amps = watts
69.6 * 25.58 = 1.780 watts

From the data sheet - the max the mppt 150/100 can output is 1450watts - so everything about that will be clipped. But times that are partially cloudy or not perfect conditions- you will have the advantage of more panels on the roof.

Did this long post answer your questions?

Yes it did. I will look into the cost difference between a single scc and running 2 scc's. Thanks!

 

[TheBreeze]

Did this long post answer your questions?

Actually, the length was extremely informative. Thank you very much.